[knolan]

These are the type of fitting used in many applications.

https://www.idex-hs.com/store/fluidics/fluidic-connections/f...

They are stupid expensive but usually work well. An alternative is to use a biopsy punch in PDMS and simply shove a 1.6mm tube into the resulting hole. The PDMS will hold the tube securely at most pressures.

[pen2l]

Neat. I see a lot of threaded components, is the expectation that at contact point we should have a threaded opening? How the heck does someone manage to do that at these micro-scales?

Also, wowza, it pains me to see non-metric units used there. One would have thought that fields that are so deeply academic in nature would be free of imperial units!

[knolan]

There are lots of different types of fittings. For glass chips where you etch the glass and bond another layer of glass over to seal you often have surface mount ports that you clamp on over a small hole and cure in an oven to bond. These give you a threaded port.

https://darwin-microfluidics.com/products/nanoport-kit-for-1...

It’s not so micro really. The internal flow geometry is around 100um but you’re mostly working with 1.6mm (1/16”) tubing that’s easily handled and used with all these fittings. The fittings are all finger tightening and a lot of the prefabricated chips are easily clamped into manifolds. You can also be creative and use heat shrink to connect tubes and the aforementioned PDMS punching works well, you just leave a large (2mm) region at the start and end of a micro channel to punch before you bond your PDMS to a glass microscope slide.

You’re never really exposing the flow geometry outside the clean room. It’s much like working with an IC on a breadboard, once it’s made you can wire it up easily and not really worry about anything mechanical other than the device working.

Yes, the imperial measurements for fittings is a pain.

My biggest complaint about microfluidics is that the design of the circuits is very ad-hoc. Since the flow rate is typically creeping flow the assumption is that the flow physics are extremely simple so we see these basic linear designs, dramatically different to microfluidic flows we see in biology. People just draw basic shapes on CAD that are easy to fabricate and iterate until the decide works.

I’ve submitted an ERC proposal to take a more computational approach to the design and layout of microfluidic devices. Instead of designing the exact layout of the device geometry the designer expresses their intent for its function, as a circuit diagram or node workflow and we then use various methods (such as numerical simulation and optimisation) to construct the geometry. I guess it’s not too dissimilar to automated PCB layout.

[pen2l]

What about a hybrid approach, as I think folks do right now more or less -- draw it out by eye, and then validate the design with simulation-software (e.g. https://www.comsol.com/microfluidics-module) and iterate as needed from thereon.

Your inclination toward a computational approach makes me think of what folks in mechanical engineering are up to these days. Creating mechanical designs generatively with topological optimization (https://all3dp.com/2/topology-optimization-simply-explained/). There appear to be clear use-cases and advantages: you reduce the amount of material needed, decide exactly what stress points you want to focus on and work to strengthen those particular parts of the structure in interesting ways, etc. Fluid mechanics is a little more complicated though I think, so you're certainly up for a challenge!

I wish you success with your proposal, and I hope to discover your findings published in a nature paper on the frontpage of HN sometime soon ;).

[knolan]

Thank you! Yes, generative design is part of it.

I’m interested in this approach because the current situation (including hybrid) has engineers, often students, designing devices to meet the need of biologists. There a going to be a fundamental challenge here in terms of communication of requirements, expertise and time the engineers have and limitations of available fabrication methods.

This results in the lowest common denominator in terms of design and performance. I want to make tools that the key stakeholders (biologists etc) can use to plot out the functionality they require and obtain a functional geometry. I’ve also got a concept for a rapid prototyping platform that eliminates many of the problems with 3D printing.